The present invention relates to power transmissions and, more particularly, to a family of transmissions having three planetary gearsets that are controlled by five torque-transmitting mechanisms to provide six forward speed ratios and one reverse speed ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier employs three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in Lepelletier is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of the present invention to provide an improved family of transmissions operating in a powertrain and being capable of providing at least six forward speed ratios and one reverse speed ratio.
In one aspect of the present invention, each family member has three planetary gearsets each consisting of a sun gear member, a ring gear member, and a planet carrier assembly member. In another aspect of the present invention, each family member includes five torque-transmitting mechanisms that are operable to control the speed ratios of the planetary gearsets. In yet another aspect of the present invention, a fixed interconnecting member continuously interconnects a first member of the second planetary gearset with a first member of the third planetary gearset. In yet still another aspect of the present invention, a second member of the third planetary gearset is continuously connected with a stationary member such as a transmission housing.
In still another aspect of the present invention, the input shaft is continuously connected with a member of the first or second planetary gearset, and the output shaft is continuously connected with a member of the first or second planetary gearset. In yet still another aspect of the present invention, the five torque-transmitting mechanisms are comprised of either five clutches, or four clutches and one brake. In a further aspect of the present invention, a first of the torque-transmitting mechanisms selectively connects a member of the first planetary gearset with either the input shaft, the fixed interconnecting member, or a member of the second or third planetary gearset.
In a yet further aspect of the present invention, a second of the torque-transmitting mechanisms selectively interconnects a member of the second planetary gearset with either the input shaft, the output shaft, the fixed interconnecting member, or a member of the first or third planetary gearsets. In a still further aspect of the present invention, a third of the torque-transmitting mechanisms selectively connects a member of the third planetary gearset with either the input shaft, the output shaft, the fixed interconnecting member, or a member of theand first or second planetary gearsets.
In yet still a further aspect of the present invention, a fourth of the torque-transmitting mechanisms selectively interconnects a member of the first, second or third planetary gearset with either the fixed interconnecting member or another member of the first, second or third planetary gearsets. In yet another aspect of the present invention, a fifth torque-transmitting mechanism selectively connects a member of the first, second or third planetary gearset with either another member of the first, second or third planetary gearset, or connects a member of the first, second or third planetary gearset with a stationary member of the transmission. In still another aspect of the present invention, the five torque-transmitting mechanisms are selectively actuated or engaged in combinations of three to establish at least six forward speed ratios and one reverse speed ratio between the input and output shafts of the transmission.